Tracy sister

What if the Tracy brothers had a 14 year old sister, who goes to East High School and is the basketball team captains girlfriend. She lives with Penny during school and only comes home during holidays. Her father is not willing to let her become a Thunderbird but what happens when trouble strikes at the island. Where is she? Is she with her brothers and father in 5 or on the island with Alan, Fermat and Tin Tin? Is she on the main land? Will she help? Will her friends help?
But she also holds a secret.What is it and will she tell her family?